The initial proinflammatory phenotype of human sepsis is rapidly replaced by sustained repression in transcription of IL-1-P, TNF-a and other innate immunity genes. Lipopolysacaride endotoxin (LPS) tolerance in blood leukocytes typifies this acquired immunosuppression. The objective of this proposal is to elucidate nuclear processes responsible of LPS tolerance. We recently published the novel observation that LPS tolerance is associated with normal activation of NFxB in the cytosol, while disruption of chromatin remodeling and NFKB p65/RelA:p50 assembly occurs on native DMA of the IL-1-P promoter in human THP-1 cells, a model faithful to the human sepsis leukocyte phenotype. Our new preliminary data provide rationale to test the mechanistic hypothesis that promoter disruption in LPS tolerance of the IL-1-(3 gene and other repressed innate immunity genes involves a negative feedback loop in which LPS inducible expression of RelB participates in limiting the assembly of a competent transcription complex. This process further depends on interuption of IKK-a promoter function, which interferes with Histone H3 S10 phosphorylation. Aim 1 will test our premise using LPS responsive and LPS tolerant THP-1 cells. Aim 2 seeks to translate mechanistic findings obtained in Aim 1 to the LPS tolerant phenotype that characterizes human sepsis, with initial focus on the RelB and IKK-a disruption paradigm. To achieve Aim 2, we will obtain purified preparations of human blood neutrophils (PMN) from participants with sepsis in our critical care units. The experimental approaches employed in Aims 1 or 2 will include: Western blots, real time mRNA analysis, transfection of THP-1 cells, siRNA knockdown, and ChIP and double ChIP assays to assess RelB, IKK-a, RelA/p65, p50 and methylation of Histone H3 K9 and phosphorylationof S10 of native IL-1-(3. The TNF-a, IL- 8, and ikB-a promoters will be assessed for specificity. Public Health Relevance: This research will identify how certain immune genes are regulated during severe human infections with failure of multiple organs. Such infections are the major cause of mortality and morbidity in intensive care units in the USA.Results from this research may guide the design of new treatments for lethal infection.